how to give legend to sublegend?

%% I wants to give legend to sublegend , as i have a program to plot between T (1*25), and output (2*25), for the values of d (1*3) for n=5.

%% again i plot the program for same data as T (1*25), and output (2*25), for the values of d (1*3) for n=10.

%% now i have six figure in a single plot, and i want to show in legend n=5 for three values of d and and n=10 for rest.

%% how could i do this.